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From: Chris Li <chrisl@kernel.org>
Date: Fri, 26 Jan 2024 13:28:23 -0800
Message-ID: <CAF8kJuPLS_1m0=4vmV8fyrQ5N6yCt-2eufBkBSF=nECsb3pU2Q@mail.gmail.com>
Subject: Re: [PATCH v2] mm: memcg: Don't periodically flush stats when memcg
 is disabled
To: "T.J. Mercier" <tjmercier@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>, Michal Hocko <mhocko@kernel.org>, 
	Roman Gushchin <roman.gushchin@linux.dev>, Shakeel Butt <shakeelb@google.com>, 
	Muchun Song <muchun.song@linux.dev>, Andrew Morton <akpm@linux-foundation.org>, android-mm@google.com, 
	Minchan Kim <minchan@google.com>, cgroups@vger.kernel.org, linux-mm@kvack.org, 
	linux-kernel@vger.kernel.org
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Hi T.J.

Acked-by: Chris Li <chrisl@kernel.org>

Chris


On Fri, Jan 26, 2024 at 1:19=E2=80=AFPM T.J. Mercier <tjmercier@google.com>=
 wrote:
>
> The root memcg is onlined even when memcg is disabled. When it's onlined
> a 2 second periodic stat flush is started, but no stat flushing is
> required when memcg is disabled because there can be no child memcgs.
> Most calls to flush memcg stats are avoided when memcg is disabled as a
> result of the mem_cgroup_disabled check added in 7d7ef0a4686a
> ("mm: memcg: restore subtree stats flushing"), but the periodic flushing
> started in mem_cgroup_css_online is not. Skip it.
>
> Fixes: aa48e47e3906 ("memcg: infrastructure to flush memcg stats")
> Reported-by: Minchan Kim <minchan@google.com>
> Signed-off-by: T.J. Mercier <tjmercier@google.com>
> Acked-by: Shakeel Butt <shakeelb@google.com>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>
> ---
>  mm/memcontrol.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index e4c8735e7c85..bad8f9dfc9ab 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -5586,7 +5586,7 @@ static int mem_cgroup_css_online(struct cgroup_subs=
ys_state *css)
>         if (alloc_shrinker_info(memcg))
>                 goto offline_kmem;
>
> -       if (unlikely(mem_cgroup_is_root(memcg)))
> +       if (unlikely(mem_cgroup_is_root(memcg)) && !mem_cgroup_disabled()=
)
>                 queue_delayed_work(system_unbound_wq, &stats_flush_dwork,
>                                    FLUSH_TIME);
>         lru_gen_online_memcg(memcg);
> --
> 2.43.0.429.g432eaa2c6b-goog
>
>